Automate the Envoy AI gateway creation

[kerthcet]

What would you like to be added:

Right now, we need to apply the envoy ai gateway manually following the https://github.com/InftyAI/llmaz/tree/main/docs/examples/envoy-ai-gateway, however, we need to create all these stuff automatically by introducing a controller.

Also the configurations are static, once the service is down, the ai gateway is unaware of this, this is not right.

Why is this needed:

• Easy to setup
• Dynamically change the envoy configurations based on the status of the services.

Completion requirements:

This enhancement requires the following artifacts:

• Design doc
• API change
• Docs update

The artifacts should be linked in subsequent comments.

[googs1025]

Do we need to define a field (in Playground or Service) to allow users to set whether to enable ai-gateway?

[kerthcet]

No, it's enabled by default, but in the future we may have different gateways, like higress or kgateway as well, we should able to configure it globally.

[kerthcet]

Should be finishe after #463

[kerthcet]

would you like to have a try? @googs1025